In the field of battery powered electronic devices, such as mobile telephone handsets, it is known for such devices to comprise multiple lighting components in conjunction with, for example, visual displays, keypads, etc. In the case of a mobile telephone handset, for example, the handset may comprise both a main display backlighting component and a keypad backlighting component. Furthermore, in the case of a ‘clam shell’ type telephone handset, where the main display is typically located within an inner surface of a hinged cover, and as such generally hidden from view when the handset is in a closed configuration, an auxiliary display of smaller size for displaying reduced information is often provided within an outer surface of the hinged cover such that the auxiliary display is visible when the handset is in the closed configuration. Accordingly, the clam shell telephone handset may further comprise an auxiliary display backlighting component.
Typically, the backlighting components are required to be activated independently, with each backlighting component comprising one or more lighting elements, such as light emitting diodes (LEDs), which may be connected in an array. The backlighting components for devices such as mobile telephone handsets are subject to various performance requirements. For example; uniformity of lighting is often required, both between the different backlighting components, as well as between the lighting elements of the same backlighting component. This is especially the case within the main display, which requires all the lighting elements in the same array to be supplied with well matched currents. In addition, low power consumption is desired in order to increase the battery life of the device. Independent luminosity control for the different lighting arrays is often a desirable feature, which requires independent programming of the LEDs' current sources for the different lighting arrays. Furthermore, independent dimming functionality for the different lighting arrays is sometimes used in backlighting components. However, these techniques require the provisioning of accurate current linearity for the programming of the LEDs' current sources.
Known backlighting controller systems that attempt to address some or all of the above performance requirements tend to require large semiconductor die area, in particular where a parallel driver is used with an individual current source for driving lighting elements within a backlighting component being connected in parallel. In addition, some backlighting controller systems require a high pin count of the integrated circuit that comprises the controller system, in particular if individual current sources are provided for each lighting element in a backlighting component. In some controller systems the use of separate voltage control modules for different lighting arrangements is excluded due to their requiring multiplication of costly self-inductances, which limits the possible usage cases for the lighting controller system, especially if more than one lighting component cannot be active simultaneously or if the luminosity of different lighting element arrays is too different.
A yet further problem associated with existing lighting controller systems occurs when several LED arrays with a different number of LEDs between the respective arrays have to be active simultaneously. The provision of current to the LED arrays in this situation, using the known techniques, results in undesirable power losses.